BANCROFT. POTENTIAL OF METALS. 113 



the same. In whicli of these three groups copper, silver, gold, and the 

 other metals belong, I cannot say, though silver is probably like mer- 

 cury. The results in Tables XI.-XIIl. open up a whole series of 

 problems to be settled by future investigators. The values for the 

 differences of the terms for any two negative ions have to be deter- 

 mined with accuracy ; the behavior of the metals Cu, Ag, etc. must be 

 examined. The work of Magnanini * shows that other relations hold 

 when the dissolved salt is an oxidizing or reducing agent, and that the 

 value ZnlRXICd, for instance, is not a function of the metals only, 

 if RX is an oxidizing agent. It is also well known that in cases 

 where the electrode metal caimot exist in the solution as ion that the 

 general relations already pointed out do not hold. From the results 

 of Negbaur -j- and of Jones J we must conclude that the term which I 

 have represented by J, B, C, etc., varies with the nature of the sol- 

 vent. The amount of this variation is entirely unknown as yet, and it 

 is equally impossible to say beforehand how a change in the solvent 

 will affect the term due to the negative ion. 



If we consider the cell ZnlZiiClolZnBralZn, the two solutions be- 

 ing assumed to be of the same concentration and dissociation, and the 

 wandering velocity of the bromine ion being further assumed to be 

 identical with that of the chlorine ion, we should expect an electromo- 

 tive force of 0.080 volt. This has not been taken into account by 

 Goodwin § in his determinations of the solubilities of silver chloride, 

 bromide, and iodide. Goodwin determined the electromotive forces of 

 the cells AglAgNO.lAgCl + KCllAg, Ag| AgNO.I AgBr + KBrlAg, 

 and AglAgNOji Agl + KIlAg. From the observed electromotive 



forces the solubilities were calculated by the formula s = if ^-^^, 



E ... 



where log cf = --^. In this equation s is the solubility, pi the con- 



centration of the Ag ions in the nitrate solutions, p^ the concen- 

 tration of the CI, Br, or I ions in the corresponding solutions, E is 

 the electromotive force of the cells, and C the integration constant, 

 which is equal at 25° to 0.0256, It is more than probable that a cor- 



* Eend. Ace. Line, VL 182, 1890. X Zeitschr. f. ph. Ch., XIV. 346, 1894. 



t Wied. Ann., XLVIL 27, 1892. 



§ Zeitschr. f. ph. Cli., XIII. 645, 1894. It is only fair to Mr. Goodwin and to 

 myself to say that I have pointed out to liim privately the objections that I made 

 to his results that he might correct them himself if he felt so inclined. He thinks 

 that it would he better for me to make my comments in print, and I have 

 accordingly done so. 



VOL. XXXI. (n. s. xxiit.) 8 



